All Questions
14
questions
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Poincaré recurrence in a closed universe? [duplicate]
Is it possible that the Poincaré recurrence applies to a closed universe (with a finite spacetime)? If it is, would this mean that a closed universe could eventually reach the same state as its ...
- 2,472
8
votes
2
answers
3k
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Do Boltzmann brain thought experiments suggest literally anything can form randomly?
Do Boltzmann brain thought experiments suggest literally anything can form randomly?
What are the limitations to what random fluctuations can form? Literally any physical, material object?
Lastly, I ...
user353810
0
votes
0
answers
40
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Is the 2nd law of thermodynamics more of a likelihood than a law? [duplicate]
Given enough time, even extremely unlikely events are certain to happen. This includes spontaneous reduction in disorder.
As an example, given enough time, all the particles of a gas in a container ...
- 1,421
2
votes
1
answer
169
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What does the arrow of time and entropy say about the universe and repetition?
This question What is the relationship between how time is viewed in thermodynamics and how time is viewed in general relativity? is close to what I was wondering, but it didn't get into repetition ...
- 123
3
votes
1
answer
1k
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Conservation of entropy in cosmology
I've been trying to follow the procedure that some books give in order to prove that the entropy of the universe is conserved (S is constant).
It usually goes like this:
Consider the second law of ...
5
votes
2
answers
797
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Can we really apply the second law to the entire universe?
I do not doubt the second law in general, just if it rigorously applied to the entire universe. Here's why I ask this
2nd law - restricted to isolated systems: "The second law may be formulated ...
- 601
60
votes
9
answers
8k
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How do different definitions of entropy connect with each other?
In many places over the Internet, I have tried to understand entropy.
Many definitions are presented, among which I can formulate three (please correct me if any definition is wrong):
Entropy = ...
- 1,137
4
votes
1
answer
280
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What happens here when the Second Law of Thermodynamics doesn't hold true?
In the 1920s, theoretical physicists, most notably Albert Einstein, considered the possibility of a cyclic model for the universe as an (everlasting) alternative to the model of an expanding universe. ...
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-3
votes
1
answer
225
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Must the origin of the universe be non-physical? [duplicate]
Since the 2nd law of thermodynamics says the universe's entropy is constantly increasing, then its initial entropy must have been smaller than it is today.
However, no known physical law can reduce ...
- 173
1
vote
1
answer
231
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Estimation of the entropy of the universe
I heard the following way to estimate the entropy of the universe:
using that the entropy is dominated by photons, in particular the cosmic microwave background radiation, which has a wavelength ...
- 9,304
-1
votes
1
answer
420
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Confusion on the concept of Boltzmann brain
I heard that a Boltzmann brain is a brain-like object that materialized from random fluctuations of particle fields, where particles randomly "pop into existence" and just so happened to form a brain.
...
- 916
9
votes
4
answers
4k
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Is heat death reversible by thermal or quantum fluctuations given an infinite time?
I'm new here, so apologies if the question doesn't sound meaningful considering what physics is supposed to answer. I don't have a physics or mathematics background, but I did learn a few things about ...
- 452
33
votes
7
answers
22k
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Why was the universe in an extraordinarily low-entropy state right after the big bang?
Let me start by saying that I have no scientific background whatsoever. I am very interested in science though and I'm currently enjoying Brian Greene's The Fabric of the Cosmos. I'm at chapter 7 and ...
Kristof Claes
2
votes
1
answer
1k
views
Does the heat death of the universe really imply a maximum entropy state *all* of the time? Or most of the time?
Statistically speaking, you're going to still encounter deviations from equilibrium, even though the expected value is equilibrium. But these rare deviations from equilibrium - which are inevitable - ...
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